1. Field of the Invention
This invention relates to a light beam scanning apparatus for making a light beam scan by use of a mechanical light deflector, and more particularly to a light beam scanning apparatus provided with a scanning position correcting means in which the detection of the angular position of the light deflector and the detection of the displacement of the light beam scanning from the correct position are conducted by a common means whereby the correction of the position is conducted simultaneously with the generation of clock signals.
2. Description of the Prior Art
Heretofore, a light beam scanning apparatus which employs a mechanical light deflector such as a galvanometer mirror, a rotating polygonal mirror, a hologram scanner or the like is widely used in the various kinds of scanning recorder or scanning reader. In this kind of light beam scanning apparatus, there sometimes occurs a displacement of the scanning position in the direction perpendicular to the scanning direction due to the error in parallelism of the deflecting facets of the mechanical deflector or the wobbling of the deflecting facets. In order to correct this kind of displacement, it has been known to optically correct the light beam displacement or to drive a mechanical correcting deflector according to the signal indicative of the displacement to deflect the light beam in the direction perpendicular to the scanning direction by the amount to correct the displacement.
In the above-described light beam scanning apparatus provided with the displacement correcting means, it becomes necessary to detect the angular position of the light deflector in order to make synchronization between the recording signal or the read-out signal and the scanning position. Therefore, in case where a light deflector for correction is provided, there are needed a correction light deflector, a means for driving the correcting light deflector and a means for detecting the angular position of the light deflector, which complicates the structure around the light deflector and enhances the cost of the light beam scanning apparatus.